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Extending transformer life with drying
SITRAM DRY – stationary transformer drying and moisture monitoring
with Transformer Lifecycle Management™ (TLM™)
Answers for energy.
Aging processes in the transformer’s insulating system:
The challenge:
The life of a transformer’s solid insulation plays a key role in determining the
transformer’s potential service life.
Along with high temperatures and
­oxidation processes, moisture is the
­primary enemy of a cellulose-based
insulation system. Experts agree that
maintaining a consistently low water
content in cellulose and oil substantially
prolongs transformer life expectancy.
Sporadic oil drying (performed, for
example, during oil purification) is not
enough in itself, because most of the
moisture is stored not in the oil but
in the cellulose.
Moisture
Oxygen
Temperature
Oil-cellulose insulation
Chemical degradation, formation
of acids, peroxides, etc.
Mechanical degradation
Lightning and switching
impulses
Accelerated aging
of insulation
Dielectric degradation
Insulation failure
Short circuits
Stationary oil and insulation drying
to extend the life of your transformer
Water content and temperature influence the oil’s break­
down voltage, as does the ageing of the liquid and solid
insulation. As a result, the moisture content of the liquid
and solid insulation has a major impact on a transformer’s
current operating conditions and service life. As years go
by, moisture content increases due to the hygroscopic
binding of air moisture, as well as cellulose and oil deg­
radation. Although these processes can’t be prevented
altogether, technology can be used to counter their
effects.
It has been shown that conventional methods involving
the short-term use of conventional oil purification systems
can’t reduce moisture to the necessary extent. With
­SITRAM® DRY, however, Siemens offers a continuously
operating “bypass” system for drying oil during operation,
where the transformer oil is continuously passed through
cartridges that absorb the moisture. The dried oil is then
fed back into the transformer.
Now that the state of equilibrium has shifted, deposited
water molecules diffuse from the cellulose insulation into
the insulating oil and the moisture content steadily drops
throughout the transformer. At the same time, the oil’s
breakdown voltage quickly returns to normal levels once
the process has begun.
Optional temperature and moisture sensors at the inlet
and outlet make it possible to monitor the drying process
and, if necessary, signal when the cartridges are ready for
replacement. Oil samples for DGA analyses can be taken
at the inlet and outlet points.
SITRAM DRY –
the video
Experience the
­functions of
SITRAM DRY in
sound and vision
Siemens extends the lifecycle of your transformer –
consistently and reliably. With Siemens’ SITRAM DRY.
2
www.siemens.com/
energy/TLM
Continuous oil drying with
SITRAM DRY produces a
­diffusion gradient between
insulating oil and cellulose
– thereby drawing the
water out of the insulation.
SITRAM DRY offers a number of advantages
over conventional drying methods.
Whereas offline methods require that all the oil be
pumped off and purified, SITRAM DRY works while the
transformer is operating. Thus, there are no downtime
costs with SITRAM DRY and labor costs are extremely low.
Instead of a sporadic reduction of moisture in the oil,
­SITRAM DRY guarantees a very low water content in oil
and cellulose over the long term.
Top quality and compliance with guidelines
Siemens has over a century of experience in transformer
manufacturing that was, of course, also put to use in the
development of SITRAM DRY. We are the only transformer
manufacturer who also produces oil drying systems and
uses them in our own transformers. We know what matters
and guarantee the top quality of every component as well
as its conformity with guidelines.
SITRAM DRY is simple to
install – including during
operation.
Factors for a long transformer life
•• Online drying
SITRAM DRY continuously draws moisture both from the
oil and from the cellulose insulation, without additional
heating or vacuum.
•• Increased breakdown voltage
SITRAM DRY returns the breakdown voltage to normal
levels after only a brief period of use.
•• Rugged, cost-effective solution
SITRAM DRY features top-quality components made
in Germany, low maintenance, and low costs.
•• Installation and operation without interruption
SITRAM DRY can be installed, operated, and maintained
while the transformer is in operation.
SITRAM DRY is part of the SITRAM family. With its modular solutions, this family of products helps you
to ensure the availability and long service life of your transformers. We work with you to develop solutions
that are perfectly tailored to your requirements.
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SITRAM DRY
Cabinet/Frame
SITRAM DRY Smart
Target segment:
Distribution transformers
with a conservator oil level
of at least 1.5 m above
ground
Target segment:
Power transformers with
a conservator oil level
of at least 2.5 m above
ground
Typical applications:
• Power distribution
and industry
• Water capacity:
2 x 1.5 liters
• Extended field
of application
Typical applications:
• Power generation
and transmission
­utilities/industry
• Water capacity:
3 x 3 liters
The right solution for the continuous
drying of transformer oil: SITRAM DRY
Modular system
SITRAM DRY is a modular concept for oil transformers of
any size that is easily adapted to individual requirements.
The system can be installed both in brand-new transformers
and in older transformers during operation. Three basic
designs are available: a frame version, a cabinet version,
and the SITRAM DRY Smart version.
In the frame version, SITRAM DRY is mounted in an open
steel frame together with optional moisture sensors. The
cabinet version is the right choice if you want both ease
of installation and protection of the drying system from
external influences. The cabinet has a pressure equaliza­
tion system, keeps out animals, and is certified for IP 55.
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Unlike the frame and cabinet versions, the SITRAM DRY
Smart version is mounted on rollers, making it easier and
more flexible to use at different locations. All three ver­
sions are designed for all standard applications and offer
you many benefits, including:
•• Automatic cartridge replacement signal
•• Self-monitoring of pump and moisture sensors
•• Leakage monitoring (optional)
•• Potential-free alarm contact (life contact) to SCADA
•• Extended field of application:
ambient temperatures (-20°C to +60°C)
SITRAM DRY Cabinet
Target segment:
Power transformers with
a conservator oil level of at
least 2.5 m above ground
Typical applications:
Power generation
and transmission
utilities/industry
Only continuous oil drying can
reduce moisture in oil and insulation
on a sustained basis.
SITRAM DRY Cabinet:
modular for enhanced
performance
SITRAM DRY Cabinet:
The system for special requirements
In addition to the three standard versions, the SITRAM DRY
Cabinet version can also be equipped with various perfor­
mance modules. These modules can be ordered separately
as needed and are especially intended for customers who
place a high premium on the protection of their plant and
their transformer because, for example, it’s located in a
substation or other location where it can’t be monitored
by personnel on a daily basis.
SITRAM DRY Cabinet serves you by acquiring and pro­
cessing operational data, reacting automatically and
appropriately to error messages, drying the transformer
until a predefined level of dryness is reached, making
information available via various message channels,
and displaying the most pertinent data simply and
straightforwardly via the built-in panel.
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Top:
Cartridges saturated
Bottom:
External leakage at top hose
Main customer benefits:
•• Reacts automatically to error messages
•• Stops drying when a defined level of dryness is reached
•• Provides current information on operating states and
measured values through text messaging and communi­
cation with SCADA system
•• Records and stores measured values using data logging
•• Provides a simple overview of operating conditions
through enhanced visualization
If a leak occurs inside or outside the cabinet, SITRAM DRY
prevents oil from leaking out of the transformer and auto­
matically shuts off the pump. SITRAM DRY informs users
of current operating states and measured values by send­
ing text messages, via the most common communication
protocols, including DNP3, Modbus, IEC 60870-5-104, etc.,
and by displaying the information on the built-in panel.
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Trial phase: bypass
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08.07. 18.07. 28.07. 07.08. 17.08. 27.08. 06.09. 16.09. 26.09. 06.10.
H₂O adsorption [liters]
1
Oil moisture [ppm]; temp. [°C]
Temperature, relative humidity [°C; %]
80
01.08. 21.08. 10.09. 30.09. 20.10. 09.11. 29.11. 19.12. 08.01.
Temperature, inlet [°C]
Relative humidity, inlet [%]
Relative humidity, outlet [%]
Temperature, inlet (°C)
Moisture, inlet [ppm]
Moisture, outlet [ppm]
H₂O adsorption [liters]
Cumulative precipitation
volume when using
­SITRAM DRY in a
44 MVA/110 kV trans­
former, 1977 model
SITRAM DRY:
More safety in the field
Comprehensive service
SITRAM DRY is an extremely rugged system that requires
little maintenance. Thanks to moisture sensors at the inlet
and outlet, the degree of cartridge saturation can be pre­
cisely determined, and replacement times predicted based
on trend analyses. And thanks to fast-release couplings,
cartridge replacement requires little effort – and is both
safe and drip-free.
Our service offerings allow you to choose the extent to
which you participate in your own oil drying. From instal­
lation and process monitoring to cartridge replacement,
we give you exactly the support you want.
Example of the drying process in practice
The normal drying process is divided into two phases.
­During the first phase, the oil’s water content is quickly
reduced (2 to 3 days in our example) and the breakdown
voltage is substantially improved.
Phase 2 is determined by the amount of moisture diffused
out of the solid insulation after it is precipitated from the
oil. The flow of moisture decreases steadily, along with
the relative humidity concentration.
In a trial (phase 3), the filter cartridges were excluded
from the cycle. During this test phase, the relative
­humidity in the oil rose steadily. Over the observed time
period of around four weeks, the moisture distribution
began to achieve a new equilibrium between the oil and
solid insulation.
In phase 4, the filter cartridges were reinserted in the oil
cycle, at which point it was once again possible to rapidly
reduce the moisture in the oil.
This trial strikingly demonstrates the duration of the
equalization processes between the solid insulation
and the oil. Once again, it stresses that temporary drying
methods do not achieve the desired effect, and that
only a stationary drying system can sustainably reduce
moisture.
TLM@siemens.com • www.siemens.com/energy/TLM
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Published by and copyright © 2014:
Siemens AG
Energy Sector
Freyeslebenstrasse 1
91058 Erlangen, Germany
Siemens AG
Energy Sector
Transformer Lifecycle Management™
Katzwanger Strasse 150
90461 Nürnberg, Germany
E-mail:TLM@siemens.com
www.siemens.com/energy/TLM
For more information, please contact
our Customer Support Center.
Phone: +49 180/524 70 00
Fax: +49 180/524 24 71
(Charges depending on provider)
E-mail: support.energy@siemens.com
Power Transmission Division
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